Stoker fired steam generating unit with double convection section



R. CHAN ET AL STOKER FIRED STEAM ,GENERATING UNIT WITH DOUBLE CONVECTION SECTION June 24, 1958 Filed Sept. 14, 1954 3 Sheets-Sheet 1 INVENTORS Char/e5 B C/zazz C'Zzar/es JY col/e ,fieceased 'A'TTORN EY June 24, 1958 c. R. CHAN EI'AL 2,840,056

STOKER FIRED STEAM GENERATING UNIT wrrn DOUBLE CONVECTION SECTION Filed Sept. 14, 1954 s Sheets-Sheet 2 I I it I 206 A'TTORNEY 2,840,056 ENERATING UNIT WITH DOUBL June 24, 1958 c. R. CHAN EI'AL STOKER FIRED STEAM c;

CONVECTION SECTION 5 Sheets-Sheet 3 Filed Sept. 14, 1954 eoooaocooac INVENTORS Char/es E Cfian Czar/mi. 71601/63 fieceased aryare SC/zamber/M BY Execu frz'x J ATTORNEY STOKER FIRED STEAM GENERATING UNIT WITH DOUBLE CONVECTION SECTIONv 1 a CharlesR. Chan, Pompton Lakes, N. J., and Charles H.

Woolley, deceased, late of Cranford, N. J., by Margaret S. Chamberlin, executrix, Cranford, N. J., assignors to The Babcock & Wilcox Company, New York, a corporation of New Jersey Application September 14, 1954,'s enn1No.'4ss,ss4

2 Claims. c1. 1 22480) This invention relates to improvements in steam generating units. One subject of improvement is concerned with high capacity stoker fired steam generating units.

For a high capacity unit, the grate area must have a high value and the invention involves thecoordinat'ion of superposed steam generating andsuperheating surfaces so related to the grate area that there, is effective steam generation and effective control of final steam temperature overa wide load range. v Spreader .stokers of high grate area are subject to concentration or laning of the combustion products arising from the stoker and such concentration or laning creates a problem as to uniformity of heat absorbing or superheating surfaces superposed with reference to the stok er. This concentration of combustion or laning ofthe gases is further intensified when, in a high capacity steamgencrating installation, oppositely arranged stokers areutilized to obtain the required grate capacity, particularly when the coal is impelled by fluid jets from positions at opposite walls of the furnace.

To overcome the above indicated concentrations of combustion products or laning of the gases arising from the stoker, the present invention involves a fuel fired vapor generating and superheating unit in which there is a particular construction of water cooled furnace having a narrowed upper portion constitutingfa rectangular furnace space with opposed gas outlets with the line .of furnace gas exit disposed at 90 to the furnace wall along which the fuel impelling jets of other similar devices are arranged. This upper narrowed furnace chamber, or portion of the furnace, creates such flow, turbulence and mixing of the combustion products arising from the lower portions of the furnacethat uniformity of combustion conditions is effected in the furnace chamber.

To attain the high total heat release for the illustrative high capacity steam generating units, the invention may involve the use of two stokers disposed alongside, with the combustion products arising therefrom passing first through a large volume radiantly heated lower furnace chamber ofa cross section corresponding to the total grate area, and then to a superposed single elongated upper furnace portion in which the uniformity of combustion conditions is attained in the "manner above indicated. I

The illustrative vapor generating and superheating unit involves an increasedpath of combustion products flow from the grate to the furnace exit to promote the effective stoker firing of the unit. t i

Increased separation of cinders or otherincombustible from the combustion gases is also promoted in the illustrative unit by the arrangement of two downflow. convection .gas passes at opposite sides of the .unit leading downwardly from turning spaces at Opposite sides of the uppermost portion of the furnace chamber. In one of these downfiow gas passes, the convection fluid heating surfaces are predominantly economizer' surfaces. The surfaces in the other downflow gas passarepredominantly superheater surfaces, and the control of superheat over a R 2,840,056 Patented June 2 1 ?58 wid'e load range is effected by variation and control of gasfiow through the different gas passes by a regulation of dampers at the .gas exits of the gas passes. For example, as the load (or rate of vapor generation) increases from a certain control point or value, the gas flow over the predominantlysuperheater gas pass would be decreased to compensate for the inherent characteristic of the convection superheater surfaces to effect an undesirably high steam temperature at certain load increases. Concomitantly, the gas flow through the predominantly economiZer gas pass would be decreased.

The illustrative steam generating and 'superheating unit also involves a secondary or high temperature superheater having two sections, one located adjacent the top of the prcdominantly'superheater gas pass,'and the other located at the top of the predominantly economizer gas pass. 'Each of these secondary superheater sections is ,L-shaped with opposite tubular portions nearest the uppermost portion of the furnace chamber and with integral horizontal portions extending across the downflow of gas at the entrance to the pertinent gas pass. Each of these L-shapedsecondary superheater sections preferably consists of U-tubes 'each with an inlet leg connected to an external inlet header, and an outlet leg connected to an external outlet header. This construc-, tion not only constitutes a drain'able superheater component, but it also involves the disposition of its vertical tubular components in a zone in which this arrangement permits the separation of solids carried in suspension by the furnace gases as they pass from the uppermost part of the furnace chamber into the pertinent gas turning space.

The invention will be concisely set forth in the claims appended hereto but for a more complete understanding oflthe invention, its mode of operation and advantages, reference should be had to the following description whichrefers to the accompanying drawings, in which a preferredembodiment of the invention is described:

'In thedrawings: v V Fig. l is mainly a vertical section through the illustrative unit, on the planes of the section line 1-1 of Fig. 2, showing the arrangement of the stoker, furnace chamber and air heater;

Fig. 2 is a vertical section taken on the line 2-2 of Fig. l and in a plane at right angles to the plane of the Fig.1 section; and p g Fig. 3 is a multiple'plane view showing the illustrative unit partially in horizontal section and partially:in plan Theillust rative unit is stoker fired and, to attain "the tions as indicated at 1214 in Fig. 2. Each stoker may be of a type involving a travelling grate 16,"receiving coal from a hopper 18 or it may involve a stoker having a non-travelling grate and having a series of coaliirn- :pelling jets'20, arranged along the furnace wall 22 and directing streams of fuel over the stoker grate'and toward the opposite. wall 24 of the lower part of the furn'ace chamber. Such jets'are associated with a hopperjin which a body of coal is maintained by other apparatus,

and the arrangementmay be of the typeindicated in the patent to Kohout 2,257,693, Sept. 30, 1941. In either case, an ash discharge device such as .26 is disposed at one end of the stoker and combustion of the fuel is promoted by the fiow of high temperature air from the air heater 30 from which ductwork including the components 3235, leads to the air inlet chamber 38 beneath the stoker grate. Combustion supporting air is thus forced upwardly through the bed of burning fuel on the stoker grate.

Above the stoker is a large volume vertically elonwater 48 tomthelower, headers. The upper ends of the vaporQgene'rating wall tubes'40 and 418.115 connected to .the' 48 through the interof {upper front and wall headers 50 and 2 and appropriate circulatorconduits leading from those headers to the drum; 6 The drum is appropriately supported by hangers 240 fromast'eel work 242in manner wellfknown in the art; I

Fig. 2

ows the sidewall vapor generating tubes 54 thefside walls of the wide lower portion of the furnace chamber generally indicated at'62; This'lower portion of the furnace chamber generally corresponds in area of and56leading froin'the lower headers 58 and 60, over boundaries of which are a from the water space of the screen tubes sections 76 and 78 on one side, and the 'similar screen tubes sections 110 and 112, on the opposite side. From an inspection of Fig. 2 of the drawings, it will be seen that some of the wall tubes 54 pass upwardly along the outerwall' 200 of the gas pass 102, and that similarly, some of thewall tubes 56 have upper extensions 202; extending along the right hand wall204 of the gaspass 66. Beyond these extensions, these tubes have roof portions 206 extending along the roof section 92 to connection with the drum 48. Similarly, the upward'extensions ofthe wall tubes 54 along the'left hand wall-V200 of the gas pass l02 have inwardly extending roof sections 210 extending alongthe roof section 212 to connection with the drum 48L The arrangement andfconstruction ofthe L-shaped secondary superheaters: with their vertical tubular secitshorizdhtal section to the grate area of the subjacent stokers, at 1 Above the lower'portion62 of, the furnace chamber,

thecsidehwall tubes 56 havejinwardly and upwardly insections 64 combining "with appropriate heat resisting material to. form 'a wall or slopingfloor for the 'gas pass 66. Beyond the inclined sections 64 the sidewall tubes leading from the header 60 have vertical sections 68 at one side of, a narrowed and vertically elongated superposed furnace chamber section 70.

Toward the tupper par't of'this'chamber the said wall tubes have inwardly and upwardly inclined sections 72 combined with appropriate heat resisting material to form- 'a sloping floor or inclined wall at the bottom of the secondary superheater space ,74. Beyond the section 72 'the'.,pertinent wall' tubes continue as a screen having upright tubular sections76 'and ,78' disposed for-' .waidlyof the upright tubular sections of the vertical 4 portion 80 of one of the secondary superheater sections.

These sections, form of an. L-shaped secondary superheater indicated at 80; having upright tubular sec- ;tions 82 integral withhorizontally extending tubular sections 84. The combined upright and vertical tubular sec ,tions constituteflthe U-tubes conductingsteam, from the inlet header 86fto the anal outlet header 88L 7 Beyond -thescreen,sections,76;and 18forwa'rdly of ,ltho secondary'superheatersection, the side wall-tubes have roof sections 90 extending over a short distance 6 th 1?? s t ws siPt aa o L unit.

At a o posite side can a the inn, as indicated in ,Fig, 2. C the side wall" tubes 54; continue upwardly through ftheIinclined tubular sections 100, which combine with clined-wall beneath the'pi'edominantly superheater gas passf102f, Beyond this position they continue upwardly 'sectio nsithe tubes continueupwardly'through the small roof sections 114 to connection with the steam and water drum48.r

The efiectsof the concentration, of combustion gases and other" suspended solids in a zone adjacent the rear 7 wall tubes 40, occasioned by, the use of spreader stokers,

is correctedmby the increased gas turbulence andmixing efiect ofthe association of the lowerwidened portion of thefurnaee-chamber' with the intermediate or superposed narrowed portion, of the furnace 70, compelling thegases rising from the stokers to converge inwardly to-thenarrowed portion ofthe furnace chamber. This effect is' further augmented by the additionally narrow uppermost portion of the furnace chamber between the 'and'by'reason of "their turning at through the gas outlets 122and 124 at the lower parts of the gas passes. The separated particlesarecollected in hopper constructions and 132 from which they are periodically removed.

Control a of superheat' .to' maintain a predetermined temperature over a widely varying 'load range, is, attained by the selective control or operation of dampers at theoutlets122 and 124 of the gas passes 66 and 102. Such dampers'are indicated at 134 in Fig. l for the gas outlet 124. Such control or proportioning of the gas flow over the two 'gas passes in response to load variations may be attained by automatic control systems which are wellknown in the art, the gas flow being controlled by operation of the dampers in response to two or more variables, including indications .of steam flow and indications 'ofjfinal steam temperature at or beyond the final outlet header 88 of the secondary superheater.

The outlet 124*of thegas pass 102 and the outlet construction 122 .of the gas pass 66, lead to a cross duct '(Fig. l).f and then through ductwork or breeching 142 to the gas "inlet of the -air heater 30. The gases flow through the horizontally spaced upright tubes 144 of the .air heater to the ductwork 146 leading to the inlet 148"0ftheinduced draft fan 150, driven by the motor 151..

Appropriately, there are dust collecting hoppers 152 and l54 disposed respectively beneath the ductwork 142 nected'byian iipright duct 224, to the outlet 226 of a fan 228, driven by a motor 230. The air outlet 232 of v the air heaterleads from the ductwork components 32-35 tol the stoker.

In the operation of the illustrative" unit, feed water entersthe unit at and proceeds through the economizer section 162 which preferably consists of serially connected horizontally extending tubes forming a bank or tubes leadingto a header at 164. From this header the partially. heated feed water flows through the exterior conduit 166 to an inlet header 168 from which the feedwater flows through the banks of convection heated tubes of the successive economizer sections 170- 172, From the outlet 174*of the latter, feedwater flows through appropriate connections'to the drum 48. The latter has appropriate vapor and liquidseparation apparatus therein acting upon the vapor and liquid mixtures discharged into the drum by the vapor generating wall tubes.

The separated vapor passes from the upper part of the drum through appropriate tubular connections, such as 173, to a header situated at the vapor inlet 175 for the primary convection superheater sections 176 and 177. From the outlet 178 of the latter, the partially superheated steam passes by appropriate connections to the inlet headers 86 and 179 of the opposite L-shaped secondary superheaters. The outlet header 180 of the secondary superheater 108 is connected by an appropriate conduit 182 to the final outlet header 88 of the superheater.

What is claimed is:

1. In a stoker fired steam generating unit, stoker means of rectangular grate area disposed near the base of the unit, a steam and water drum symmetrically arranged in the upper end of the unit, pairs of oppositely arranged upright exterior walls extending vertically upward from said stoker means in a uniform rectangular horizontal cross-section substantially corresponding to the grate area of said stoker means, steam generating tubes defining a pair of spaced walls disposed interiorly of the enclosure formed by said upright walls and combining therewith to form a pair of downflow gas passes at opposite sides of and wholly within said enclosure, said spaced walls also defining a vertically elongated upper furnace chamber section between and opening to the upper end of said downflow gas passes, the spaced walls terminating at their lower ends in laterally extending arches within the enclosure at positions intermediate the height of the unit and substantially superjacent the stoker means, steam generating tu-bes extending upwardly along said upright exterior walls, said last named tubes and the tubes defining said spaced walls having their upper ends connected to said steam and water drum, steam superheater tubes arranged in one of said downflow gas passes, economizer tubes arranged in the other of said gas passes, and dampers arranged to control the gas flow through each of said downflow gas passes.

2. In a stoker fired steam generating unit, stoker means of rectangular grate area disposed near the base of the unit and arranged to move a fuel bed therein, a steam and water drum in the upper end of the unit, pairs of oppositely arranged upright exterior walls extending vertically upward from said stoker means in a uniform rectangular horizontal cross-section generally corresponding to the grate area of said stoker means, steam generating tubes defining a pair of spaced walls disposed interiorly of the enclosure formed by said upright walls and combining therewith to form a pair of downflow gas passes at opposite sides of and wholly within said enclosure, said spaced walls being arranged parallel to one another and to the direction of fuel travel in said stoker means, said spaced walls also defining a vertically elongated upper furnace chamber section between and opening to the upper end of said downflow gas passes, the spaced walls terminating at their lower ends in laterally extending arches within the enclosure at positions intermediate the height of the unit and substantially superjacent the stoker means, steam generating tubes extending upwardly along said upright exterior walls, said last named tubes and the tubes defining said spaced walls having their upper ends connected to said steam and water drum, steam superheater tubes arranged in one of said downflow gas passes, economizer tubes arranged in the other of said gas passes, and dampers arranged to control the gas flow through each of said downflow gas passes.

References Cited in the file of this patent UNITED STATES PATENTS 

